The present invention relates to working machines which include an engine functioning as a drive source of a machine""s working section and an electric motor functioning as a drive source of a machine""s moving or transporting section.
In recent years, there have been developed new-type working machines where a machine""s working section and transporting section are driven by separate drive sources. Typically, the working section is driven by an engine, while the transporting section is driven by an electric motor. Because the rotation of the motor that drives the transporting section can be controlled as desired, the new-type working machines can make relatively sharp small turns and thereby move relatively agilely.
Among examples of such new-type working machines is a xe2x80x9cself-propelled lawn mowerxe2x80x9d disclosed in Japanese Patent Laid-open Publication No. HEI-3-43013 (hereinafter also called a xe2x80x9cdisclosed prior art mowerxe2x80x9d). In the disclosed prior art mower, a lawn mowing cutter is driven by an engine, front wheels are driven via a transporting drive motor powered by a battery, and the rotation of the transporting drive motor is controlled by a controller.
However, the disclosed prior art mower, where the transporting drive motor is powered by the battery alone, can work only for a limited time. In addition, the battery must be of a great capacity, which therefore has to be large in size and heavy in weight. Mounting such a large and heavy battery on the working machine of a relatively small size is not advisable.
As one solution to the problem of the disclosed prior art mower, it is thinkable to use the above-mentioned engine to drive not only the mowing cutter but also an electric power generator so that the battery can be charged by the power generator, and use the power generator and battery as the power source for the transporting drive motor. In this case, the transporting drive motor can be driven by the power generated by the power generator alone, and the remainder of the power generated by the power generator can be stored in the battery. This way, the battery may have a smaller size, which can advantageously reduce the necessary space for mounting the battery on the mower and the overall weight of the mower as well. In addition, the mower is allowed to work for a very long time.
Generally, a small-size engine is used to drive the mowing cutter or other working section which is subjected to only small loads. However, the working machine is often operated with its traveling speed greatly varied in accordance with actual working conditions. For example, even when the small-size engine is being rotated at low speed with a small throttle opening, the transporting drive motor may be accelerated rapidly to quickly achieve a high-speed transporting state.
Since the transporting drive motor is driven by the electric power generated by the electric power generator at any time, the generator is required to generate more electric power as necessary acceleration of the transporting drive motor increases. As the necessary electric power increases rapidly, the loads on the engine also increase rapidly. If the loads on the engine rapidly become excessive, the number of rotations of the engine would be reduced to a considerable degree. Further, the reduced number of the engine rotations would reduce the number of rotations of the mowing cutter, so that the working efficiency of the mower would be lowered undesirably.
To maintain a desired number of rotations of the engine, it is only necessary to adjust the throttle valve opening by manually operating an engine throttle lever. In this case, however, operating the engine throttle lever each time the transporting drive motor is to be accelerated or decelerated through operation of a transporting speed lever is very bothersome, and some improvement has to be made to enhance the operability of the working machine.
In view of the foregoing prior art problems, it is an object of the present invention to provide a working machine where a working section and electric power generator are driven via an engine and the power generator and battery chargeable by the power generator are used as power sources of a transporting electric motor, and which can accelerate the electric motor with necessary acceleration while effectively restricting a rapid increase of loads on the engine.
It is another object of the present invention to provide a working machine where a working section and electric power generator are driven via a small-size engine and the power generator is used as a power source of a transporting electric motor, and which can readily maintain a desired number of rotations of the engine in response to acceleration or deceleration of the electric motor and thereby achieve enhanced operability.
It is still another object of the present invention to provide a working machine where a working section and electric power generator are driven via an engine and the power generator is used as a power source of a transporting drive motor, and which can accelerate the electric motor with necessary acceleration while effectively preventing a rapid increase of loads on the engine.
According to a first aspect of the present invention, there is provided an improved working machine which comprises: a driving section including an engine, an electric power generator driven by the engine, a battery chargeable by the electric power generator, and an electric motor (transporting electric motor) drivable by both of the electric power generator and the battery; a working section driven by the engine to perform desired work; a transporting section driven by the electric motor; and a control section for controlling rotation of the electric motor, on the basis of a comparison between an actual transporting speed and a target transporting speed of the transporting section. In the present invention, the control section performs the operations of: determining necessary acceleration of the transporting section in accordance with a current actual transporting speed of the transporting section; determining a correction coefficient corresponding to a current number of rotations of the engine, from among correction coefficients having a characteristic of becoming closer to a value of one as the number of rotations of the engine increases but becoming closer to zero as the number of rotations of the engine decreases; multiplying the necessary acceleration by the determined correction coefficient, to thereby provide corrected necessary acceleration; and controlling the rotation of the electric motor in accordance with the corrected necessary acceleration.
When the number of rotations of the engine is relatively great, i.e., when the engine is rotating at relatively high speed, the rotation of the electric motor can be accelerated in the present invention in accordance with a value close to the necessary acceleration having been determined in accordance with the current actual transporting speed of the transporting section. When, on the other hand, the number of engine rotations is relatively small, the rotation of the electric motor can be accelerated in accordance with the corrected necessary acceleration of a relatively small value. Therefore, the rotation of the electric motor can be accelerated in accordance with optimum necessary acceleration corresponding to the current number of rotations of the engine.
Thus, even when the electric motor has been accelerated rapidly while the engine is rotating at low speed, the acceleration of the motor can be restricted to an optimal value corresponding to the number of rotations of the engine, and thus the amount of power generated by the power generator can also be restricted appropriately. Consequently, loads on the engine can be lessened appropriately. Namely, in the present invention, it is possible to increase the rotating speed of the electric motor with the necessary acceleration while effectively preventing a rapid increase of the loads on the engine. By thus preventing a rapid increase of the loads on the engine, it is possible to avoid an undesired reduction in the number of rotations of the engine, thereby enhancing the operating efficiency of the working section.
According to a second aspect of the present invention, there is provided an improved working machine which comprises: a driving section including an electric motor, an electric power generator, and an engine having a throttle valve associated therewith; a transporting section driven by the electric motor and including a speed lever for setting a target transporting speed of the transporting section to a desired speed value, part or whole of electric power necessary for the electric motor being supplied by the electric power generator; a working section driven by the engine to perform desired work, the electric power generator being driven by the engine; and a control section for controlling rotation of the electric motor so that an actual transporting speed of the transporting section equals the target transporting speed. When the amount of electric power to be generated by the electric power generator has increased in response to a variation or increase in the necessary number of rotations of the electric motor corresponding to an increase in the target transporting speed designated by a human operator, the control section in the present invention controls the opening of the throttle valve, in order to secure the necessary number of rotations of the engine for securing the amount of electric power to be generated.
When the number of rotations of the electric motor is to be increased, more electric power is required, so that the amount of the electric power to be generated by the power generator also has to be increased. To secure the required electric power, it is necessary to acquire more than a predetermined number of rotations of the engine. For this purpose, the present invention is arranged to automatically control the opening of the throttle valve by means of the control section. With such arrangements, the present invention can readily maintain the necessary number of rotations of the engine, and eliminate the need for manipulating an engine throttle lever each time the electric motor is to be accelerated or decelerated by manipulation of the speed lever. As a consequence, the operability of the working machine of the invention can be enhanced to a significant degree.
Further, when the number of rotations of the electric motor is reduced and thus the power generator only has to generate a less amount of electric power, the load on the engine can be lessened accordingly, so that the engine does not have to operate at high speed. Therefore, the control section in the present invention automatically reduces the opening of the throttle valve. Because, in this case, the engine does not have to continue operating at high speed unnecessarily, it is possible to not only save the fuel and but also prolong the life of the engine. In addition, the present invention can effectively prevent the number of rotations of the engine from being undesirably reduced due to a great load imposed on the engine when a great amount of electric power has to be secured, with the result that the operating efficiency of the working machine can be enhanced to a significant degree.
According to the second aspect of the present invention, the control section preferably performs the operations of: determining necessary acceleration in accordance with a current actual transporting speed of the transporting section; when the opening of the throttle valve has reached a predetermined upper limit opening value, determining a correction coefficient corresponding to a current number of rotations of the engine from among correction coefficients having a characteristic of becoming closer to a value of one as the number of rotations of the engine increases and becoming closer to zero as the number of rotations of the engine decreases; when the opening of the throttle valve has not yet reached the upper limit opening value, setting the correction coefficient at the value of one; multiplying the necessary acceleration by the correction coefficient, to thereby provide corrected necessary acceleration; and controlling the rotation of the electric motor in accordance with the corrected necessary acceleration.
When the necessary number of rotations of the electric motor has increased, the control section automatically increases the opening of the throttle valve as long as the engine still has sufficient room or capacity to produce higher outputs, in order to supply necessary electric power corresponding to the increase in the number of rotations. As a consequence, the rotation of the electric motor can be accelerated in accordance with a value close to the necessary acceleration determined in correspondence with the current actual transporting speed of the transporting section.
When, on the other hand, the opening of the throttle valve has reached the upper limit opening value and the engine no longer has sufficient room or capacity to produce higher outputs, the rotation of the electric motor is accelerated in accordance with the corrected necessary acceleration of a relatively small value. Thus, the rotation of the motor can be controlled with optimal acceleration corresponding to the number of rotations of the engine. By the acceleration of the motor being thus restricted to an optimal acceleration value corresponding to the number of rotations of the engine, the amount of power generated by the electric power generator can also be restricted appropriately. Consequently, the loads on the engine can be lessened appropriately. Namely, in the present invention, it is possible to increase the rotating speed of the motor with the necessary acceleration while effectively preventing a rapid increase of the loads on the engine. By thus preventing a rapid increase of the loads on the engine, it is possible to avoid an undesired reduction in the number of rotations of the engine, thereby enhancing the operating efficiency of the working section